In the continuous casting of steel a cast steel strand continuously leaves the casting mold with a relatively thin skin of solidified steel containing molten steel, the strand traveling through a series of rollers which support the skin on opposite sides of the strand, cooling progressively causing the skin to thicken by solidification of the molten steel until a solid steel strand is obtained.
It is desirable to stir the molten steel within the skin, for example, to prevent the formation of pipe and dendrites.
For such stirring the Alberny et al U.S. Pat. No. 3,882,923 suggests that some of the skin-supporting rollers be made tubular and internally provided with an electrical inductor structure which, when provided with multi-phase AC, forms a traveling magnetic field in the molten steel within the skin, thereby inductively stirring the molten steel. Anyone unfamiliar with the principles of inductively stirring molten metal can be informed via that patent.
The prior art has also suggested the use of nonrotative stationary electric inductive stirrers positioned between the skin-supporting rollers which must then be undesirably widely spaced to provide room for these stirrers. These fixed stirrers operate on the same inductive stirring principles described by the Alberny et al patent.
The above non-rotative type of stirrer has the advantages that its design and construction are simplified and a more rugged and reliable construction is possible, but there is the disadvantage that the rollers which must support the skin of the continuously cast strand, must be widely spaced at the stirrer so that the skin support at those locations is lost. The rotative type of the Alberny et al patent have the advantage that the strand skin is continouously supported by closely interspaced rollers but have the disadvantages of complexity of construction, a lack of the ruggedness of the fixed or non-rotative type, and introduce design complications because the space inside such a stirring roller is limited by the internal diameter of the tubular roller.